Nuclear physics

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The nuclear physics is that part of the field of physics that deals with the structure and behavior of atomic nuclei busy. While atomic physics deals with the physics of the atomic shell , the subject of nuclear physics is the elucidation of the nuclear structure , i.e. the details of the structure of the atomic nucleus. For this purpose, for example, spontaneous transformations of the nuclei ( radioactivity ), scattering processes on nuclei and reactions with nuclei are examined.

The high-energy physics and particle physics have formed from nuclear physics out and therefore were previously counted with her; the actual nuclear physics was then sometimes referred to as low- energy nuclear physics to differentiate . The reactor physics grew out of nuclear physics out.

The technologies based on nuclear fission (see nuclear technology ) for the use of nuclear energy and for weapons purposes have developed from certain research results in nuclear physics. But it is misleading to call this technical-economic-political area “the nuclear physics”.

description

Nuclear physics is carried out both theoretically and experimentally. Your most important theoretical aid is quantum mechanics . Experimental tools are e.g. B. particle detectors and radiation detectors , particle accelerators and vacuum technology .

The task of “pure” nuclear physics in the sense of basic research is to elucidate and explain the nuclear structure , i.e. the details of the structure of the atomic nuclei.

From the study of radioactivity and reactions with nuclei, many applications have developed, for example

One imagines nuclei as a - in the simplest case spherical - collection of protons and neutrons.

Typical orders of magnitude in the area of ​​atomic nuclei and nuclear processes are

  • Lengths: 1  Fermi = 1 fm = 10 −15 m
  • Energy: 100  keV to 100  MeV

The building blocks of the nuclei are the nucleons : neutrons and protons . The number Z of protons in a nucleus is equal to the number of electrons in the neutral atom. Z determines the chemical properties of the atoms and is therefore called the atomic number (or, based on the atomic nucleus, also the atomic number). The mass of the atomic nucleus is determined by the number A of all nucleons and is therefore also called the mass number . As you can see, the neutron number N  =  A  -  Z . Types of atoms with the same atomic number but different numbers of neutrons are called isotopes of the respective element. The physical properties of the nucleus depend on both the atomic number and the neutron number, the chemical properties (almost) only on the atomic number.

When describing nuclear reactions and scattering processes, the term cross-section is important. The cross-section for a certain process is a measure of the probability that this process will occur in individual cases.

history

Antoine Henri Becquerel , Pierre Curie and Marie Curie received the 1903 Nobel Prize in Physics for their experiments on radioactivity, which could be described as the historic beginning of modern nuclear research .

Radioactivity is mostly associated with the conversion of one chemical element into another. This was discovered by Ernest Rutherford , for which he received the Nobel Prize in Chemistry in 1908 .

The Rutherford scattering experiment , in which alpha particles are scattered on gold foil, by Geiger , Marsden and Rutherford in 1909 marks a turning point in the idea of ​​the structure of atoms. Rutherford's interpretation of the results led to the idea of ​​the atomic nucleus . Almost the entire mass of the atom is united in the nucleus, but it only takes up a very small proportion of the volume of the atom.

In 1917, Rutherford achieved the first artificial element conversion by bombarding nitrogen with alpha radiation : oxygen was created . It was the nuclear reaction 14 N (α, p) 17 O.

The understanding of the binding energy of atomic nuclei, first expressed semi-empirically in 1935 in the Bethe-Weizsäcker formula , represented a decisive advance. The basis for the formula was the droplet model of the atomic nucleus (Bohr 1936). With the help of the Bethe-Weizsäcker formula it could be shown that energy is released in certain nuclear fusions as well as in certain nuclear fission . The droplet model is capable of z. B. to explain nuclear fission well.

A quantum mechanical description of the nucleus structure, which can explain the stability of the nuclei, which changes systematically with atomic and mass numbers, was only found later with the shell model (Wigner, Goeppert-Mayer and Jensen 1949). An important scientific journal in this field is Nuclear Physics .

Nuclear fission

Otto Hahn and his assistant Fritz Straßmann discovered in December 1938 that irradiation with neutrons split uranium nuclei (induced nuclear fission ). It was later demonstrated that a large amount of energy and further neutrons are released during this process, so that a fission chain reaction and thus the release of technically usable amounts of energy is possible in a short time, i.e. at high power . Research into the use of this energy for civil or military purposes then began, roughly at the same time as the Second World War . In Germany, among others, Carl Friedrich von Weizsäcker and Werner Heisenberg worked on the development of a nuclear reactor ; the possibility of a nuclear weapon was seen, but not seriously pursued, because the foreseeable development period seemed too long for the ruling war. In Los Alamos , the physicists Enrico Fermi , Hans Bethe , Richard Feynman , Edward Teller , Felix Bloch and others conducted research in the Manhattan Project under the direction of Robert Oppenheimer . Although this project served the development of weapons from the beginning, its findings also led to the construction of the first nuclear reactors used for energy generation.

Public discussion

Hardly any other area of ​​physics has fueled public discussion more because of its ambivalence between peaceful and destructive use: for critics of progress, nuclear physics was Pandora's box , and for those who believe in progress, it was one of the most useful discoveries of the 20th century. Nuclear fission technology was the trigger for a new ethics of science ( Hans Jonas , Carl Friedrich von Weizsäcker ). The political debate about the sensible and responsible use of nuclear energy continues to this day in the debate about Germany's nuclear phase-out .

Eminent nuclear physicists

See also

Web links

Wiktionary: Nuclear physics  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Ernest Rutherford: Collision of α particles with light atoms. IV. An abnormal effect in nitrogen , Philosophical Magazine 37, 1919, pp. 581-587. ( Publication text )